In one form of moulded commutator, the bars are retained by being embedded, together with reinforcing rings, in plastics material, which is moulded in position under pressure and fills completely all the available space. By this means, radial movement of the commutator bars under centrifugal load is more uniform than in commutators of built-up construction although such movement will still occur.
The moulded commutator above described gives adequate performance at moderate speeds. However, with present trends towards higher commutator surface speeds the shortcomings of the moulded construction are an embarrassment and even with final machining taking place at the normal running speed of the motor and with the commutator assembly heated to its normal running temperature, minute variations in the final positions of the commutator bars still occur, sufficient to cause rapid brush wear and sparking and consequent radio interference.
The moulded construction is applied to radial commutators as well as to the cylindrical type. The same limitations apply to radial commutators as apply to the cylindrical form.